The research hypothesizes that smoking is associated with gonadal impairments in young adult men and women. The hypothesis will be tested in samples from three different populations: 1. Forty young adult males without known illness; 2. One hundred husbands of infertile couples; and, 3. One young adult females without known illness. An increase in the ratio of the production of estradiol to testosterone is hypothesized in healthy young adult males who smoke, compared to nonsmokers. An increased incidence of testicular varicocles and an increased incidence of impairments of seminal fluid indices is hypothesized among the smoking husbands of infertile couples compared to nonsmoking husbands. Higher levels of serum estradiol are also predicted in smoking husbands of infertile couples. In a preliminary study of such husbands, a significant negative correlation was observed between serum estradiol levels and impairment in seminal fluid indices. Metabolic clearance and production rates of estradiol and testosterone, and seminal fluid indices will be evaluated in 40 smoking infertile husbands, before and after half of them have stopped smoking for six months. Cessation of smoking is expected to reduce estradiol production, and to improve seminal fluid indices. A greater incidence of anovulation is expected in 50 regularly menstruating women who smoke compared to a like a number of similar nonsmoking women. Anovulation will be assessed from basal body temperature records and blood progesterone levels. Higher blood testosterone levels are also predicted in the smoking women. If the hypotheses of the proposed work can be confirmed, they should provide a strong argument as to why young adult males and females should not smoke.